\begin{tikzpicture}
    \pgfmathsetmacro{\ab}{1.5}
    \pgfmathsetmacro{\ac}{3.5}
    \tkzDefPoints{0/0/B,  3.5/0/C}
    \tkzInterCC[R](B,\ab)(C,\ac)  \tkzGetFirstPoint{A}
    \tkzInterCC[R](B,\ac)(C,\ab)  \tkzGetFirstPoint{D}
    \tkzInterLL(A,C)(B,D)  \tkzGetPoint{O}

    \tkzDrawPolygon(A,B,C)
    \tkzDrawPolygon(D,C,B)
    \tkzLabelPoints[above](A,O,D)
    \tkzLabelPoints[below](B,C)
\end{tikzpicture}

